Easton's 1897 Bible Dictionary:

Hagar
   flight, or, according to others, stranger, an Egyptian, Sarah's
   handmaid (Gen. 16:1; 21:9, 10), whom she gave to Abraham (q.v.)
   as a secondary wife (16:2). When she was about to become a
   mother she fled from the cruelty of her mistress, intending
   apparently to return to her relatives in Egypt, through the
   desert of Shur, which lay between. Wearied and worn she had
   reached the place she distinguished by the name of
   Beer-lahai-roi ("the well of the visible God"), where the angel
   of the Lord appeared to her. In obedience to the heavenly
   visitor she returned to the tent of Abraham, where her son
   Ishmael was born, and where she remained (16) till after the
   birth of Isaac, the space of fourteen years. Sarah after this
   began to vent her dissatisfaction both on Hagar and her child.
   Ishmael's conduct was insulting to Sarah, and she insisted that
   he and his mother should be dismissed. This was accordingly
   done, although with reluctance on the part of Abraham (Gen.
   21:14). They wandered out into the wilderness, where Ishmael,
   exhausted with his journey and faint from thirst, seemed about
   to die. Hagar "lifted up her voice and wept," and the angel of
   the Lord, as before, appeared unto her, and she was comforted
   and delivered out of her distresses (Gen. 21:18, 19).

     Ishmael afterwards established himself in the wilderness of
   Paran, where he married an Egyptian (Gen. 21:20,21).

     "Hagar" allegorically represents the Jewish church (Gal.
   4:24), in bondage to the ceremonial law; while "Sarah"
   represents the Christian church, which is free.


Hitchcock's Bible Names Dictionary (late 1800's):

Hagar, a stranger; one that fears